1. Field of the Invention
The invention relates to fuel injectors and, more particularly, relates to a method of converting jerk type injectors to accumulator type injectors and to accumulator type injectors thus tomed.
2. Discussion of the Related Art
Jerk type fuel injectors are well known and, indeed, have been the standard in the industry for years. Jerk type injectors are non-accumulator type fuel injectors characterized by their connection to a cyclically activated pump and by the fact that injection begins with the supply of fuel to the injector above a designated pressure level (usually determined by an injector needle return spring) and terminates when fuel pressure as supplied by the pump drops below the designated level. Examples of such injectors are distributed commercially by NAVISTAR under the Part No. 1817126C91 and Standyne under the Part No. 780321.
Accumulator type fuel injectors, although, available for some time, have gained increased acceptance in recent years because they permit more precise control of fuel injection timing and quantity and generate a more efficient falling rate fuel spray than is possible with jerk type injectors and thus can significantly reduce exhaust emissions and provide improved fuel economy. Accumulator type fuel injectors are typically characterized by the use of (1) an accumulator in fluid communication with the nozzle and (2) a control cavity which is located above the upper end of the needle and the pressurization and depressurization of which are electronically controlled by a solenoid valve. Injection begins, after charging of the accumulator by a pump or by a common rail supply source, by venting the control cavity through suitable actuation of the associated solenoid valve. Fuel injection terminates when lifting forces imposed by the pressure in the nozzle cavity and accumulator drops below closing forces imposed by a needle return spring and by the then-diminished fluid pressure in the control cavity. Injection systems employing accumulator type fuel injectors are disclosed, e.g., in U.S. Pat. No. RE 33,270 and U.S. Pat. No. 5,241,935 to Beck et al.
One limitation of currently available accumulator type fuel injectors is that they are structurally significantly and in some instances fundamentally different from the more standard jerk type injectors. Jerk type injector manufacturers are thus reluctant to retool for accumulator type injector manufacturing, particularly for small production volumes. Moreover, conversion of existing jerk type injection systems to accumulator type injection systems currently requires the complete replacement of each of the jerk type injector units with an accumulator type injector unit. Such replacement renders conversion costs prohibitive in many instances.